2006 Thunderhill 25-Hour

In our fourth try, we go for victory in a pair of BMW 335 diesels!

No, we haven't lost our minds. We are going racing with a diesel-powered car to, well, to see if it's as much fun as racing a gas-powered car. When it comes to racing, fun is determined to a large extent by success, and we've seen a bit of diesel racing success lately. Not only did Audi win Le Mans and Sebring this past year with a diesel-powered sports car, the R10, but totally dominated this year's ALMS series.

But Audi wasn't the first to post a noteworthy diesel victory. In 1999, BMW set the stage for all this by winning the 24-hour race at the famous Nurburgring with a 320 diesel sedan.

It was that victory that made us think of campaigning a diesel BMW at this year's NASA 25-hour event at Thunderhill Raceway in northern California. Both the Thunderhill and Nurburgring events are populated mostly by modified production cars. And both are long-distance events with an emphasis on reliability and fuel economy, as well as speed. It seemed the perfect opportunity to evaluate first-hand the potential advantages of a diesel-powered race-car. In Europe, diesels have long made up a large percentage of the passenger-car fleet, and have become even more popular over the past 10 years because fuel (both diesel and gasoline) is more than twice as expensive as it is in America and, over there, diesel is generally cheaper than gasoline. As a result, economic considerations have driven the upsurge in diesel sales.

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But not even stingy Europeans would have gone for diesels as heavily as they have—roughly half of all vehicle sales are diesel these days—if modern oil burners didn't perform so well. Thanks to the latest turbocharger and high-pressure common-rail injection technology, 21st-century diesel engines are quiet, relatively emissions free, and generate a great deal of low-end torque. They work particularly well with automatic transmissions, but even some manual transmission drivers prefer them due to their tremendous low-end performance.

Once we decided to explore diesels for this race, we had basically the whole range of European cars open to us. We obviously wanted good speed, excellent handling, rock-solid reliability, and the best possible fuel consumption. These requirements pointed towards a diesel car that was both lightweight and powerful.

As we examined our options, the BMW 330d started looking very good. We've had long experience with the 3-series sedan and great respect for its excellent all-around handling. It's also a fairly light and efficient car. Its single-turbo 3.0-liter diesel six-cylinder engine develops 228 hp at 4000 rpm and 369 pound-feet of torque at 1750 rpm. That's down 27 ponies, but up 149 pound-feet from the American 330i about which we've written so lovingly. And on the European fuel economy cycles, that diesel delivers 20-25 percent better fuel economy, depending on your transmission choice. As we pondered this car, we learned that BMW was planning an even more powerful version for 2007. The Bavarian company was developing a 335d by fitting the twin-turbocharged version of the 3.0-liter diesel six from its 5-series sedan into the 3-series four-door. According to BMW, this engine develops 282 hp at 4400 rpm and a massive 428 pound-feet of torque at 1750 rpm, numbers that were backed up during dyno testing (see below) where the 335d produced 232 hp and 378 pound-feet at the wheels.

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We approached BMW with our idea for the race and the company was very excited. Like many European manufacturers, BMW is planning to bring diesel-powered cars to America over the next few years, for all of the predictable reasons. But BMW is particularly interested in proving that its diesel models will deliver the performance and driver involvement that have made the firm's gasoline-powered models so successful. Competing at Thunderhill would be a good way to start proving this.

We decided on a two-car team with a total of eight drivers. Four of us would be Car and Driver staffers including Executive Editor and very experienced vintage racer Mark Gillies, Senior Editor and long-time SCCA competitor Tony Swan, Technical Director and SCCA competitor Larry Webster, and your rusty racer and humble Editor-in-Chief. All four of us have competed in the first three Thunderhill 25-hour events, and Swan and I have a total of 43 24-hour events between us.

BMW nominated pro racers Bill Auberlen and Joey Hand as well as Martin Birkmann, the Motorsports Manager for BMW of North America. Rounding out the team will be Auston Harris (below right), a 15-year-old racer who has demonstrated great talent and maturity far beyond his years.

We know Harris is good because he and I co-drove together to a third-place finish in last year's Thunderhill 25-Hour event. The team manager for that effort was Marshall Pruett and we enlisted Marshall and his Marshall Pruett Motorsports Engineering to prepare the cars and organize this 2006 effort as well.

With the race less than one month away, Marshall is working overtime to get the two cars ready, but we've persuaded him to post a few photos and captions of the cars as he transforms them from refined street cars into dedicated racing machines. Expect regular updates and videos from our early practice sessions as well as regular reports from the race, which takes place on the weekend of December 1-3. Practice and qualifying take place on Friday, and the race is scheduled to start at 11:00 am on Saturday.

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On Monday, November 13th, the Car and Driver/BMW team went to Thunderhill for the first track test of the just-completed BMW 335d race car. In usual race-car fashion, the folks at Marshall Pruett Motorsports Engineering were up all night putting the finishing touches on the car.

Assisting them in this task were three people from BMW. Stefan Schnabel and Rudolf Huber journeyed all the way from BMW's Diesel Engineering center in Steyr, Austria to help with the powertrain. Stefan is an electronics expert thoroughly familiar with the car's engine management system, while Rudi is the technician who assembled the engine in the car shown in these photos. He's been working on BMW diesels for some time. In fact, he also assembled the engine in the BMW 320d that won the 24-Hour Nürburgring race in 1998.

Also on hand was James Hunt from BMW North America. Everyone assumed that James showed up to crack the whip, but we were pleasantly surprised when he changed into work clothes and pitched to twist wrenches and get greasy during the all-nighter.

I, of course, heard all about this second hand, having flown into San Francisco late Sunday night. When I got to the track Monday morning, the car had just been unloaded and looked very sanitary. Joey Hand, one of BMW's American LeMans drivers was on hand to perform the key shakedown duties, while I hoped to get a few dozen laps behind the wheel to get familiar with the car and relearn Thunderhill.

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Unfortunately, it was pouring rain for the entire day, making it impossible to achieve any serious lap times or make meaningful fuel consumption measurements. Furthermore, we had a couple of electrical glitches that were likely minor, but still prevented the braking system from operating properly.

We did learn that the diesel is remarkably hushed around the track. Even at full song on the front straight, the sound of the air being displaced is louder than any noise the engine makes. And this is without any mufflers on the car, though the particulate traps remain in position. Though we experienced some electrical glitches during the test, no major problems cropped up and the car performed solidly.

Now the order of business is to iron out the teething problems and finish assembling the second car. No problem—there's almost a week left before the race on Saturday.

Meanwhile, check out the photo gallery that reveals the car and the modifications made to turn it into a racer.

Under the hood lies the 335d powerplant. It's a 2993cc inline-six-cylinder diesel with four valves per cylinder, double-overhead camshafts, and a very high-pressure, computer controlled common-rail fuel injection system. In stock form it develops 282 hp at 4400 rpm and 428 pound-feet of torque at 1750 rpm.

This is fundamentally the same engine as the 330d, except that it uses two turbochargers rather than one. Furthermore, the two turbos are staged, with the smaller one providing the boost at lower rpm, switching to the larger turbo at higher revs. Peak boost pressure is about 23 psi. For the Thunderhill race, BMW engineers have increased the boost pressure somewhat but, other than that, the engine is largely stock.

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Note the cylinder with the yellow band on it just behind the dipstick. That's the remote reservoir for the left front Moton shock absorber. The reservoir for the right front shock is just forward of the air cleaner housing.

This unfortunately blurry image shows the stout roll cage that has been built into the car by MPME's partners, Impact Engineering. Based on the European factory WTCC BMW E90 cages, MPME and Impact made logical changes to the design to best suit American cage standards.

It is particularly stout in the A-pillar areas, with the thickness extending directly towards the driver, which improves bending stiffness while minimizing interference with cornering visibility. Also note how the side tubes extend into the door cavity to provide maximum crush space for protecting the driver from a side impact.

The Recaro racing seat provides tremendous lateral support and it's mounted on the stock seat track to accommodate the different sized drivers on the team. The stock steering column, which both tilts and telescopes also helps everyone to achieve an ideal driving position.

Though the stock instruments remain, we have mounted an auxiliary panel from Corsa A.N., using the Race Technology GPS-based digital dash. It not only provides the ability to monitor the powertrain's critical pressures, but it also includes adjustable shift lights. In the center of the instrumental panel, where the original iDrive screen once resided, will be an auxiliary panel with the controls for the specialized lights and other dedicated racing devices.

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Willows, California, Dec. 1 — It's December again, and you know what that means, right?

Correct — that special time of year when a gathering of gritty gearheads celebrate the end of the racing season with the longest race of them all: the NASA 25 Hours of Thunderhill.

This will be the fourth renewal of this unique National Auto Sport Association classic, and the fourth time a Car and Driver contingent has been on hand to participate.

As in our previous twice-round-the-clock runs, we've reached a bit to field something a little unusual for this unusual race, in this case a pair of BMW 335 turbodiesels, described in our first Thunderhill update filed in mid-November.

In that report, we were cautiously optimistic. In this update, as we count down to the 11 a.m. (Pacific) starting time, we are simply cautious.

Owing largely to a late project start, neither of the two Bimmers has had as much development as we would have liked, particularly our No. 34 car, whose first on-track foray consisted of a handful of laps during Friday's practice and qualifying.

To oversimplify a bit, the developmental culprit was getting the BMW brake control computers to accept the substitution of racing brakes for the standard system.

Even after a number of adjustments, the consequence is brake systems that are extremely touchy and lockup-prone, which bodes but ill for lap times and tire wear.

On the other hand, the Bimmers are BMW agile, and we expect the turbodiesel engines to deliver what diesels are good at: superior fuel economy, which could add up to about three hours between pit stops, versus the hour-and-half typical of some of the fast cars in the field.

In addition to fuel-thrifty, these diesels are also extraordinarily quiet. At idle, the differential cooling fans emit more noise than the engines, and when the cars are hustling down the Thunderhill front straight the only really identifiable sound is from the tires.

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Endurance and fuel economy are obviously key factors in long races, but having a fast car is certainly helpful.

In that sense, two cars stood out at the end of conclusion of Friday's brief qualifying session.

The quickest car in the field was a 2004 Porsche 911 GT3, led by Kevin O'Connell from Newport, Beach, California. Porsches have won all three Thunderhill 25s, and this one has to figure as the pre-race favorite.

Only a second back of the O'Connell car is a Mazda-powered sports-racer fielded by the Alliance Financial team from Palo Alto, California.

Unlike the O'Connell Porsche, this is a purpose-built race car with an open cockpit, plastic bodywork, and very low curb weight. The problem with cars answering this description in years past has been reliability, but the Alliance team members naturally hope that their car will be different in this respect.

Hope, of course, is a key component in all racing endeavors, and we, like the guys behind the Alliance team, hope for the best with our Bimmers.

For the record, the Car and Driver diesels will start fifth and 13th in a field that has shrunk from 62 cars officially entered at the start of the week to some 50-plus at the conclusion of Friday qualifying.

We are unable to be more precise with the count, since some of the cars had problems with their transponders — all timing in the 25-hour is handled electronically — and will thus have to start at the back of the field. This includes the 1974 Lost 'n Spaced Porsche 911 that won the race outright last year.

As in the past, we'll furnish periodic updates during the race, the first of them somewhere between two and three hours into the event. So do not — repeat not — stray far from this space.

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Willows, California, Dec. 2 — The 2006 NASA Thunderhill 25-hour race is a little over an hour and a half old, and it's time to report the activities of the two crews supporting the twin Car and Driver BMW turbodiesels engaged in this day-plus classic.

The crew of the number 33 car, which started fifth overall, is sitting on its collective hands, waiting for their car's first scheduled pit stop.

That car, with pro racer Joey Hand at the wheel, is circulating easily in third place overall, and second in its class.

The crew of the number 34 car, however, is much busier, twisting wrenches under the Bimmer's hood as they prepare to extract the engine and swap it for the spare engine stashed in the team transporter.

Number 34 started from the 13th grid position, and with veteran BMW racer Bill Auberlen manning the pedals had worked its way up to seventh when the engine abruptly stopped emitting power and began emitting smoke.

The bad news: it became instantly clear that the Bimmer's turbodiesel was finished.

The good news: this occurred only 20 minutes into the race, leaving lots of time for the engine swap and a return to combat.

Okay, that's not really very good news. But it's all the news we have at the moment, because we don't have any specifics on the engine failure.

Meanwhile, as predicted, the Kevin O'Connell Porsche 911 GT3 is running away from the field, pursued by the Alliance Financial Mazda-powered sports-racing car.

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The race thus far has proceeded at a strong pace without any caution-flag incidents. How long will that last? And how long will the crew of number 34 be working their wrenches?

We'll report on these and other matters of interest in future updates.

Willows, California, Dec. 2 — The race has reached the eight-hour milepost, which is pretty close to one-third the distance.

Expressed in linear terms logged by the leading car — the O'Connell Racing Porsche 911 GT3 that's set the pace since the green flag waved this morning — that adds up to 230 laps or 690 miles.

Although there have been occasional caution periods for stalled cars, the O'Connell Porsche is nevertheless on track to record the fastest NASA Thunderhill 25-Hour yet run.

With good weather conditions — cool and dry — plus Porsche's endurance race reliability record, that record looks like a lock.

And if the O'Connell Porsche should stumble, the Porsche 911 of defending champ Lost 'n Spaced Racing, running a solid second 10 laps back, is ready to pounce.

Not bad for a 32-year-old race car.

Third place, we're happy to report, still belongs to one of the two Car and Driver BMW 335 turbodiesels, although it's currently under heavy pressure from the Alliance Financial Mazda sports racer, making a comeback from a lengthy stop for mechanical repairs.

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We're also happy to report that the second Car and Driver BMW is back in the fight after its early four-hour stop for an engine replacement.

Four hours may seem like a long time — it certainly seemed like a long time to the car's drivers — but it's remarkably quick for a remove-and-replace engine job in a production-based automobile.

Even stripped down for racing, a production car is a far more complex critter than a purpose-built racing machine, with lots of extra plumbing and wiring and sub-systems that all have to be disconnected and reconnected.

Then there's the always-exciting moment of starting up the new engine and waiting to see whether the computer is going to accept it and deliver full power. Think of it as the automotive equivalent of a heart transplant, minus the tissue-matching phase.

Once the swap was complete, the crew pulled the cylinder head off the dead diesel and found two holy pistons, plus a valve with a little wedge-shaped piece missing from its rim.

None of these maladies enhance performance, and the two Austrian crew members who have some experience with these new engines were at a loss to explain the failures.

But after their display of expertise during the engine swap, we see them as heroes nevertheless.

Willows, California, Dec. 3 — Like Alice in Wonderland running at top speed merely to stay in the same place, the status remains quo as this 25-hour race rolls into its second half.

The O'Connell Racing Porsche GT3 continues to draw away from all its pursuers, the Alliance Financial Mazda sports racer has battled its way back to second place overall, the Lost 'n Spaced Porsche runs in third, and the Car and Driver 335d BMW turbodiesel holds down the fourth spot, slowly pulling away from the Pacific Power Motorsports team, which is campaigning yet another Porsche 911, this one vintage 1995.

If there's any surprise in all of this, it's the performance of the Alliance Financial Mazda, which has been consistently fast since a long repair stop early in the race.

As we speak, the leading car has covered a remarkable 385 laps, or 1155 miles.

The fourth-place C/D entry rolls along 27 laps in arrears, with 1074 miles to its credit, while the second C/D Bimmer, continuing in comeback mode after its engine transplant, has worked its way to 46th place with 675 miles on its race clock.

In all, 56 cars took the green flag yesterday morning. It's always difficult to gauge attrition in this race, since cars long presumed dead suddenly reappear to log a few more miles, but only four teams have definitely called it quits at this point, a remarkably light attrition rate.

The race has also been remarkably free of crippling incidents. There have been a few fender-wrinkling encounters, but no really severe crashes.

Long may it last.

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Willows, California, Dec. 3 — There's this theory that slow and steady wins the race, but someone apparently forgot to tell Kevin O'Connell and the rest of the O'Connell Racing crew.

Starting from pole position, O'Connell's 2004 Porsche 911 GT3 Cup race car set a blistering pace in the 2006 NASA 25 Hours of Thunderhill, and led every lap en route to a record-setting victory.

The car is no stranger to this event, having been part of the one-two Porsche finish staged by the Flying Lizard team in the 2003 25-hour inaugural.

O'Connell acquired the car with this race in mind as a tuneup for the February 24-hour race at Daytona. And like the Flying Lizard run, his Thunderhill effort was distinguished by exceptionally thorough preparation, superb crew support, and fast, error-free driving by O'Connell, Craig Stanton, Greg Fordahl, Jason Bowles, Mike Speakman, and Berisha Betim.

Although the second-half of the race was slowed by a couple of lengthy caution periods to sort out crashes, dry track conditions and a flawless car allowed the O'Connell team to log 705 laps — 2115 miles — over the course of the race.

That's 120 miles more than the previous race record, set last year by the defending champion Lost 'n Spaced team in their veteran 1974 Porsche 911.

Although Lost 'n Spaced couldn't match the pace of the O'Connell car, they too exceeded their previous best distance, covering 1995 miles to finish second.

Third went to the Mazda-powered sports racer of Alliance Financial, which overcame numerous minor problems to come on strong at the end, winding up just two laps shy of the previous race record.

The victim of the Alliance Financial finishing sprint was the No. 33 Car and Driver BMW 335d turbo diesel, which had held down third place overall through most of the second half of the race.

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But as the laps wound down, the Bimmer's right rear shock absorber began refusing to shoulder its share of the suspension load, making the car all but unmanageable in the final half-hour of the race.

Nevertheless, with pro driver Joey Hand keeping the car mostly on the pavement, Team C/D was able to hang on for third in its class and fourth overall, with 1965 miles on the odo.

Considering the development problems encountered over the weekend, it was a remarkable finish.

The second C/D Bimmer didn't fare quite as well. In addition to a blown engine in the first hour of the race, the 335d took a resounding whack in the right rear from a 2007 Acura TL fielded by Honda Research, requiring suspension work that consumed a half-hour late in the race.

The Acura car was assessed penalty time by NASA officials, but that did nothing to improve the BMW's chances for a finish in the top half of the field.

Instead, the much-abused 335d wound up 32nd overall, with 463 laps (1389 miles) to its credit.

Nevertheless, despite numerous problems, we were solidly impressed by the performance potential of the new BMW turbo diesel engines, which we may see in U.S. 3-series Bimmers as early as 2008.

In all, some 48 cars (of 56 starters) were running at the finish, although many of these were cripples that emerged during the final few laps to limp around to the checkered flag.

For a more comprehensive recount of this memorable race, see the March issue of Car and Driver.